1. Field of the Invention
This invention relates to hydrocarbon fuels for high speed aircraft and missiles where the fuel is used in cooling the vehicle and the engine.
2. Description of the Related Art
The state of the art of using hydrocarbon jet fuels to cool engine or vehicle components is much as it has been since the development of the gas turbine engine for aviation. The fuel is primarily used to cool the engine oil and is usually limited to temperatures below 300.degree. F. The realistic limitations of hydrocarbons with regard to their capability to cool high-speed aircraft or missiles has never been determined. The use of JP7 fuel in the SR71 demonstrated the fact that a hydrocarbon fuel produced from petroleum, could effectively be used in a high-speed aircraft where the fuel would reach temperatures near 600.degree. F. prior to combustion. The Air Force has been investigating the use of hydrocarbons at even higher speeds in both aircraft and missiles over the last 30 years. Techniques for improving the fuel's heat sink capability as the speeds of aircraft increased have been studied. About 25 years ago the USAF began looking at catalytically enhanced endothermic reactions with the dehydrogenation of naphthenes over platinum on alumina catalyst being the most successful. Efforts have been aimed at increasing the activity and the geometric configuration of the catalyst, in order to reduce weight. A total heat sink on the order of 2000 BTUs per pound could be obtained using this approach. However, there are problems in that the catalyst system adds weight and complexity to the aircraft fuel system. For instance, there are limitations on the usable temperatures of the catalyst, and a secondary cooling fluid is needed to transfer heat to the catalyst system. Also, there are pressure drops associated with the efficient use of the catalyst although current research is investigating the coating of catalyst on heat exchange tubes.